Estimated β_mn coefficients for an ionized gas with electron temperature of 10⁴ K for electron densities between 10² and 10¹² cm^-3. The solid and dashed lines show the β_mn values derived by Storey & Hummer (1995) for H30α and H38β transitions, respectively. We note that the H38β lines thermalize at electron densities lower than for H30α lines.